A variety of touch panel technologies are presently in existence, including resistive technology, capacitive technology, surface acoustical wave (SAW) technology, infrared (IR) technology, etc.
In the case of IR touch panel technology, infrared emitter/collector pairs are used to project an invisible grid of light a small distance over the surface of the panel. When a beam is interrupted, the absence of the signal at the collector is detected and converted to touch coordinates (e.g., X/Y rectangular coordinates). Since the method of determining a touch is optical instead of electrical or mechanical, IR touch panels are not as sensitive to damage as some technologies, such as resistive and capacitive technologies.
The structure of a conventional optical touch panel is disclosed in U.S. Pat. No. 6,597,508, which is incorporated herein by reference. FIG. 1 depicts the construction of a conventional optical touch panel 101 as shown in the patent. The optical touch panel 101 comprises a plurality of light-emitting elements (e.g., LEDs) 110 arranged along two adjacent sides of a rectangular position-detecting surface 150 and a plurality of light-receiving elements (e.g., photo transistors) 130 arranged along the other two sides of the rectangular position-detecting surface 150 such that the light-emitting elements 110 are positioned opposite to the respective light-receiving elements 130 and the position-detecting surface 150 is positioned between the light-emitting elements 110 and the light-receiving elements 130.
A control block 140 causes the light-emitting elements 110 to emit light beams sequentially from left to right and from top to bottom, and causes the light-receiving elements 130 to receive light beams from the respective light-emitting elements 110 positioned opposite thereto. The light beams of the light-emitting elements 110 are sequentially scanned across the position-detecting surface 150 such that optical paths are formed on the position-detecting surface 150 in a grid pattern.
The touch coordinates can be determined in accordance with which light-emitting element 110 emits a light beam and which light-receiving element 130 senses such light beam during a scan cycle. When an object (e.g., a pointing device such as a touch pen or a finger) 170 is positioned on the position-detecting surface 150 as shown in FIG. 1, the object 170 blocks some optical paths to thereby hinder light beams from the corresponding light-emitting elements 110 from reaching the corresponding light-receiving elements 130 positioned opposite to the light-emitting elements 110. As a result, the control block 140 determines the position of the object 170 in terms of two-dimensional coordinates (e.g., X/Y rectangular coordinates) based on information of received light beams from the light-receiving elements 130. If the object 170 also blocks the infrared light of adjacent rows and columns of the grid pattern, the intended center position can be obtained by averaging the coordinate information received by the relevant computing device.
In the optical touch panel 101, however, the light-emitting elements 110 and the light-receiving elements 130 must be arranged along the four sides of the position-detecting surface 150, and hence it takes a significant amount of time to establish wire connections among the elements. Thus, the optical touch panel 101 is complicated, its assembly difficult, and it is difficult to reduce its size.
FIG. 2 depicts the construction of another conventional optical touch panel 201 as shown in U.S. Pat. No. 6,597,508 that attempts to resolve the aforementioned issue.
The optical touch panel 201 comprises light-emitting elements 210, two reflectors 220 (e.g., mirrors) for reflecting lights from the light-emitting elements 210, and light-receiving elements 230 for receiving the reflected lights from the reflectors 220.
The light-emitting elements 210 and the light-receiving elements 230 are alternately arranged along two adjacent sides of a rectangular position-detecting surface 250, and the reflectors 220 are arranged along the other two adjacent sides of the rectangular position-detecting surface 250.
When an object 270 lies in a position shown in FIG. 2, the object 270 blocks some optical paths to thereby hinder lights from the reflectors 220 from reaching the light-receiving elements 230 opposed to the object 270. As a result, a control block 240 determines the position of the object 270 based on information of received lights from the light-receiving elements 230.
The optical touch panel 201 thus may have simpler wiring, a simpler assembly, and a smaller size than the optical touch panel 101. However, the optical touch panel 201 uses a pair of alternately arranged elements (i.e., a light-emitting element 210 and a light-receiving element 230) per one optical path, and thus the resolution (i.e., accuracy) of the touch panel will be affected. For example, the four positions A, B, C, and D in FIG. 2 have the same X/Y coordinates, and thus resolution will be affected.
Additionally, the aforementioned optical touch panels require a light gate for each light-receiving element in order to prevent erroneous light detection from being caused by sunlight. Therefore, a solution is needed that is able to increase the resolution while preventing erroneous detection from sunlight.